Icebergs are among na。ture's most spectacular creations, and yet most people have never seen one. A vague air of myst。ery envelops them. Th。ey come into be。ing -----。 somewhere ---。---in faraway, frigid waters, amid thunderous noise and splashing turbulence, whi。ch in most cases no one hears or sees. They exist o。nly a short time and then slowly was。te awa。y just a。s unnoticed.
Objects of sheerest beauty they have been call。ed. Appearing in an endless variety of shapes, they may be dazzlingly white, or they may。 be glassy blue, green or purple, tint。ed faintly of in d。arker hues. T。hey ar。e graceful, stately, inspiring ----- in calm, sunlight seas.
But they are a。lso call。ed frightening and dangerous, an。d that they are --。-- in th。e night, in the fog, and in storms. Even in clear weather one is wise。 to stay a safe distance away from them. Most of their bulk is hi。dden b。elow the wate。r, so thei。r。 underwater pa。r。ts may extend out far beyond the visible top. Also, they ma。y rol。l over unexpectedly, churning t。he waters aroun。d them.
Icebergs are parts of glaciers that break off, drift into the water, floa。t about awhile, and finally melt. Icebergs afloat today are made of snowflakes that have fallen ove。r long ages of time. They embody snows tha。t drifted down hundreds, or many thousands, or in some cases maybe a million years ago. The snows fell in polar regions and on cold mountains, where they melted only a l。ittle or not at all, and so collec。ted to great depths over the years and c。enturies.
As each year's snow accumulation lay on。 the surface, evaporation and melting caused the snowflakes slowly。 to lose their feathery points and become tiny grains of ice. When new snow fell on top o。f the old, it too tur。ned to icy grains. So blankets of snow and ice grains mounted layer upon layer and we。re of such。 great thickness that th。e weig。ht of the upper layers compressed the lower ones. Wit。h time and pressure from above, the many small ice grains joined and changed to larger crystals, a
  下一页<